In WCF, can data contract classes inherit from one another?

Question

In a WCF service, I have two classes with the [DataContract] attribute. One of these classes has an "is-a" relationship with the other - so class B can inherit from class A. However, when I configure inheritance between these two classes, both denoted with a [DataContract] attribute, the metadata fails to load when testing the services.

Is this possible in WCF? Am I missing another attribute?

[DataContract]
public class A
{        
    [DataMember]
    public MyCustomType AValue1{ get; set; }

    [DataMember]
    public MyCustomType AValue2 { get; set; }
}

[DataContract]
public class B: A
{    
   [DataMember]
   public double BValue1{ get; set; }

   [DataMember]
   public double BValue2 { get; set; }
}

NOTE: The custom types are also defined using data contracts.

UPDATE: Below is the error:

Error: Cannot obtain Metadata from http://localhost:8002/GISDataServices/mex If this is a Windows (R) Communication Foundation service to which you have access, please check that you have enabled metadata publishing at the specified address. For help enabling metadata publishing, please refer to the MSDN documentation at http://go.microsoft.com/fwlink/?LinkId=65455.WS-Metadata Exchange Error URI: http://localhost:8002/GISDataServices/mex Metadata contains a reference that cannot be resolved: 'http://localhost:8002/GISDataServices/mex'. Receivera:InternalServiceFaultThe server was unable to process the request due to an internal error. For more information about the error, either turn on IncludeExceptionDetailInFaults (either from ServiceBehaviorAttribute or from the <serviceDebug> configuration behavior) on the server in order to send the exception information back to the client, or turn on tracing as per the Microsoft .NET Framework 3.0 SDK documentation and inspect the server trace logs.HTTP GET Error URI: http://localhost:8002/GISDataServices/mex There was an error downloading 'http://localhost:8002/GISDataServices/mex'. The request failed with HTTP status 400: Bad Request.

UPDATE 2: See my answer below.

Answer 1

Yes, but you need to decorate the base class with the [KnownTypeAttribute] constructing it with the derived class's type. For instance:

[DataContract]
[KnownType(typeof(B))]
public class A
{
   [DataMember]
   public string Value { get; set; }
}

[DataContract]
public class B : A
{
   [DataMember]
   public string OtherValue { get; set; }
}

Answer 2

Based on this test it should work fine. Do both classes have Default Constructors? Are you using Auto-Properties. Note, In this basic sample the Attributes aren't required. Also, as David Morton mentioned you depending on which element you're returning you may need the KnownType attribute, I'm not 100% but the known type might have to go on the operation contract.

class Program
{
    static void Main(string[] args)
    {
        var serializer = new DataContractSerializer(typeof(Employee));

        var employee = new Employee() { Name="Joe", Salary=100000  };
        using (var ms = new MemoryStream())
        {
            serializer.WriteObject(ms, employee);

            ms.Position = 0;

            var newEmployee = serializer.ReadObject(ms) as Employee;
        }

        Console.ReadKey();

    }
}

[DataContract]
public class Employee : Person
{
    [DataMember]
    public decimal Salary { get; set; }
}

[DataContract]
public class Person
{
    [DataMember]
    public string Name { get; set; }
}

[ServiceContract]
interface IEmployeeService
{
    [OperationContract]
    Person GetPerson();

    [OperationContract]
    Employee GetEmployee();

    [OperationContract]
    [KnownType(typeof(Employee))]
    Person GetEmployeeAsPerson();
}

Answer 3

Okay, I figured out the question. The answer is...I'm an idiot. It had nothing to do with inheritance. In the base class, I had a data contract member without a 'set' property clause - only a 'get'. Doh!!! Putting in a 'set' clause made it work like a charm.

Sorry for the confusion.